1. Field of the Invention
The present invention relates to an optical annealing method for obtaining a semiconductor layer of high quality, and a method for producing a semiconductor device utilizing said semiconductor layer.
2. Related Background Art
In the field of crystal growing technology for growing a thin crystalline film on an amorphous substrate, there has been proposed a solid phase growing method consisting of heat treating an amorphous thin film, formed in advance on a substrate, at a temperature lower than the melting point, thereby transforming said film to a crystalline state.
For example, it was reported that large lamified polycrystals of the order of a micron could be formed by applying heat treatment to a thin silicon film, the film having been formed on an amorphous insulating substrate and having been made amorphous by ion implantation, for several tens of hours at 600.degree. C. in a N.sub.2 atmosphere. Transistors of satisfactory characteristics could be formed thereon (T. Noguchi, H. Hayashi & H. Oshima, 1987 Mat. Res. Soc. Symp. Proc., 106, Polysilicon and Interfaces, 293, Elsevier Science Publishing, New York, 1988).
Additionally, for improving the characteristics of the thin film and the device, methods of irradiation with an ultraviolet laser and with an infrared lamp have been proposed (T. Noguchi et al., Japanese Laid-Open Patent No. 61-289620) (Igano and Tani, Richo Technical Report No. 14, p. 4, Nov. 1985).
These two methods using lamp heating to deposit a thin Si film on a quartz substrate superpose so that a Si wafer in contact with said Si film. This causes said Si wafer to absorb the light of the lamp transmitted by said quartz substrate and said thin Si film, and to heat said thin Si film on said quartz substrate by conduction of the generated heat. These methods have the drawbacks of insufficient or uneven contact in microscopic scale, contamination, fusing etc. resulting from the superposing of a heat absorbing member.
For example, it is well known that the silicon wafer has modulations of several microns, even in the smoothest state. It is, therefore, impossible to obtain complete contact by superposing said Si wafer on the thin Si film so that the heat received by said thin Si film is inevitably uneven. As a result, the heated thin Si film generates an uneven temperature distribution therein, and such unevenness in temperature becomes an obstacle in obtaining a uniform structure in the crystal, and eventually affects the characteristics of the device in an undesirable manner. Further, if the temperature is raised close to the melting point, fusion of the thin Si film and the Si wafer serving to absorb the irradiating light may result, so that the device manufacturing process cannot be initiated.